With the development of wireless communication technology, new network forms are continually emerging for wireless communication network, such as Worldwide Interoperability for Microwave Access Forum (WiMax) network and Wireless Local Area Network (WLAN) developing rapidly nowadays. Typically the wireless communication network includes Customer Premises Equipments (CPEs), Network Access Providers (NAPs) built by different operators, and Network Service Providers (NSPs). The WiMax network will be taken as an example in the following description, and the WiMax network based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16 can provide relatively high access rate.
FIG. 1 is a schematic diagram showing a reference model of a WiMax network in the case of non-roaming. In the situation of non-roaming, an Access Service Network (ASN) 110 connects with a Connection Service Network (CSN) 120, and a Subscriber Station/Mobile Subscriber Station (SS/MSS) 130 accesses the CSN 120 through the ASN 110.
FIG. 2 is a schematic diagram showing a reference model of a WiMax network in the case of roaming. In the situation of roaming, an ASN 110 connects with a Visited Connection Service Network (Visited CSN) 121, and the Visited CSN 121 connects with a Home Connection Service Network (Home CSN) 122. An SS/MSS 130 gets authenticated at the Home CSN 122 through the ASN 110 and the Visited CSN 121, and uses services provided by the Visited CSN 121 and the Home CSN 122.
In general, ASN belongs to NAP and CSN belongs to NSP. In a practical deployment, NAP, Visited Network Service Provider (Visited NSP) and Home Network Service Provider (Home NSP) may be run by different operators, meanwhile there may be an overlapping area covered by multiple ASNs and each ASN may connect with several NSP networks. At present, there are two different deployment modes for WiMax network: one is NAP+NSP mode, i.e. the relationship between NAP and NSP is one-to-one, and the other is ASN sharing mode, i.e. there are roaming protocols between one ASN and multiple NSPs, and one ASN is shared by multiple NSPs.
FIG. 3 illustrates possible deployment modes for WiMax network.
ASN 111 of NAP_4 and ASN 112 of NAP_6 cover an overlapping area. CSN 1201 of NSP_1, CSN 1202 of NSP_2 and CSN 1203 of NSP_3 share the ASN 111 of the NAP_4; the ASN 112 of the NAP_6 and CSN 1204 of NSP_6 are bound together; SS/MSSes 131 and 132 access the network through the ASNs 111 and 112 respectively.
In the ASN sharing mode, CPE would encounter a problem: how to know by which NSPs the current ASN is shared, i.e. how to know which NSPs may be used through the current ASN. This is a problem regarding NSP selection present in a wireless communication network, i.e. how network-side provides information about the current available networks to the CPE, so that the CPE may further obtain information about all the NSPs accessible at the current position so as to select an NSP to access a network.
In the prior art, discovering NSPs in a wireless communication network is implemented by setting a broadcast message. For example, Service-Identity-Information is carried in a broadcast message, as specified in the current IEEE 802.16 protocol, and Base Station (BS) may use the broadcast message to broadcast the information about the accessible NSPs periodically on its own initiative. Table 1 shows information elements in the broadcast message.
TABLE 1SyntaxSizeNotesService-Identity-Information format ( ) { Management Message Type =8 bits To Be Assigned TLV encoded InformationVariablesTLV specifics(See Table 2)}
The TLV contained in the above broadcast message at least includes one or more NSP identities. NSP identity is defined in a TLV way as shown in Table 2.
TABLE 2TypeLengthValueTo-Be-AssignedTo-Be-DefinedNSP identity
According to this approach, when performing NSP discovery, an SS/MSS listens to the broadcast message from the BS and receives NSP information carried in the broadcast message transmitted by the BS periodically. If the waiting time is too long, the SS/MSS may also request the BS to broadcast the relevant NSP information by using the broadcast message. For example, the SS/MSS may request the BS to transmit the relevant broadcast message on its own initiative by carrying the information element as showed in Table 3 in a RNG-REQ message.
TABLE 3TypeLengthValueTo-Be-Assigned1NULL character
If the RNG-REQ message carries the above information element, then this means that the SS/MSS requests the BS to transmit the information about the supported NSP list; otherwise, there is no such a request.
The above method for implementing NSP discovery by transmitting NSP information by means of message broadcasting has the following problems:
Since one period is needed to broadcast an NSP list, the SS/MSS needs to wait for a period of time to receive the relevant broadcast message, which will cause a considerable delay; if the relevant broadcast message is transmitted during a short period of time, then more air interface resources are needed to transmit the relevant message, which will cause a waste of downlink air interface resource; and if the transmitting of the relevant broadcast message is requested by the SS/MSS, then a random access resource is occupied, which will cause a waste of uplink air interface resource.